HIBERNATION. 



775 



rose to 91; and turning it up to the liver, to 

 93. 



" The animal being replaced in the cold 

 atmosphere at 30, for an hour, the thermome- 

 ter was again introduced into the belly ; at the 

 liver it rose to 93; in the pelvis to 92; the 

 mouse continuing very lively. 



" It was again put back into an atmosphere 

 cooled to 19, and left there an hour; the ther- 

 mometer at the diaphragm was 87; in the 

 pelvis 83; but the animal was now less 

 lively. 



" Having been put into its cage, the thermo- 

 meter being placed at the diaphragm, in two 

 hours afterwards was at 93." * 



In these experiments the animals appear to 

 have been roused partly by the state of the 

 wound in the abdomen, but chiefly by the ex- 

 treme cold. They can scarcely, however, be 

 considered as experiments upon hibernation, 

 however interesting they may be in reference to 

 reviviscence from that state. 



The fact of the fatal influence of excited re- 

 spiration during the augmented irritability of 

 hibernation, contrasted with the similar fatal 

 effect of suspended respiration, during the dimi- 

 nished irritability of the state of activity, will 

 illustrate many of the causes, kinds, and phe- 

 nomena of death. Do not these resolve them- 

 selves, in fact, into irritability insufficiently or 

 excessively excited ? 



IV. Of torpor from cold. It is highly im- 

 portant, and essential to the present investiga- 

 tion to distinguish that kind of torpor which 

 may be produced by cold in any animal, from 

 true hibernation, which is a property peculiar 

 to a few species. The former is attended by a 

 benumbed state of the sentient nerves, and a 

 stiffened condition of the muscles ; it is the 

 direct and immediate effect of cold, and even 

 in the hibernating animal is of an injurious and 

 fatal tendency; in the latter, the sensibility and 

 raotility are unimpaired, the phenomena are 

 produced through the medium of sleep ; and 

 the effect and object are the preservation of 

 life. 



Striking as these differences are, it is certain 

 that the distinction has not always been made 

 by former observers. In all the experiments 

 which have been made, with artificial tempera- 

 tures especially, it is obvious that this distinc- 

 tion has been neglected. 



True hibernation is induced by temperatures 

 only moderately low. All hibernating animals 

 avoid exposure to extreme cold. They seek 

 some secure retreat, make themselves nests or 

 burrows, or congregate in clusters, and, if the 

 season prove unusually severe, or if their retreat 

 be not well chosen and they be exposed in con- 

 sequence to excessive cold, many become be- 

 numbed, stiffen, and die. 



In our experiments upon hibernation we 

 should imitate nature's operations. Would any 

 one imagine that the following detail contained 

 the account of an experiment upon this sub- 

 ject ? " Le 31 Janvier," says M. Saissy, " a 

 trois heures du soir, la temperature atmosphe- 



* Animal (Economy, pp. Ill, 112. 



rique etant a l-25 au-dessous de zero, celle 

 d'un herisson engourdi profondement a 3'50 

 au dessus, j'enfermai ce quadrupede dans un 

 bocal de verre entoure de toute part d'une mix- 

 tion de glace et de muriate de soude. L'exces 

 du froid le reveilla d'abord, mais trois heures 

 ont suffi pour le replonger dans une profonde 

 torpeur. 



" J'avais place 1'animal de rnaniere que je 

 pouvais repeter, autant que je le jugeais neces- 

 saire, les experiences thermometriques. Des 

 que sa temperature cut baisse jusqu'a zero, (ce 

 ne fut qu'a 2 heures du matin) je le retirai du 

 bocal et le placai dans une temperature de 12 

 et plus au dessus de la glace ; mais 1'animal 

 e"tait mort." * 



To induce true hibernation, it is quite neces- 

 sary to avoid extreme cold ; otherwise we pro- 

 duce the benumbed and stiffened condition to 

 which the term torpor or torpidity may be 

 applied. I have even observed that methods 

 which secure moderation in temperature, lead 

 to hibernation : hedgehogs, supplied with hay 

 or straw, and dormice, supplied with cotton- 

 wool, make themselves nests and become lethar- 

 gic ; when others, to which these materials are 

 denied, and which are consequently more ex- 

 posed to the cold, remain in a slate of activity. 

 In these cases, warmth or moderated cold ac- 

 tually concur to produce hibernation. 



When we read of insensibility, of a stiffened 

 state of the muscles, and of a cessation of the 

 circulation, as obtaining in hibernation, we may 

 be certain that a state of torpor has been mis- 

 taken for that condition. The actually hiber- 

 nating animal exposed to continued severe cold 

 is, as M. Saissy correctly observes, first roused 

 from this state of ease and preservation into a 

 painful activity, and then plunged into a fatal 

 torpor. 



This subject will come to be considered in a 

 subsequent part of this inquiry, in which I 

 purpose to trace the effects of cold in changing 

 the relative quantity of respiration and degree 

 of the irritability in animals of different ages 

 which do not hibernate ; in the meantime, the 

 accurate distinction between mere torpor, which 

 may occur in any animal, and which is a de- 

 structivestate, from true hibernation, which is 

 preservative, and the peculiarity of certain ani- 

 mals, will enable us to correct many inaccuracies 

 into which Legallois,f M. Edwards,^ and other 

 physiologists have fallen. (See IRRITABILITY.) 



In conclusion, one of the most general effects 

 of sleep is to impair the respiration, and with 

 that function the evolution of animal tempera- 

 ture. The impaired state of the respiration in- 

 duces a less arterial condition of the blood, 

 which then becomes unfit for stimulating the 

 heart; accumulation of the blood takes place 

 in the pulmonary veins and left auricle ; a 

 sense of oppression is induced, and the animal 

 is either roused to draw a deep sigh or awakes 

 altogether. 



* Recherches stir les Animaux hibernans, par 

 M. J. A. Saissy, pp. 13, 14. 



f (Euvres de Lcgallois, Paris, 1824, p. 282. 

 f Agens Physiques, pp. 148, 292. 



